use hash of comm_tag if not numeric

examples/wave/wave-op-mpi.py

@@ -192,10 +192,7 @@ def main(ctx_factory, dim=2, order=3,
     else:
         actx = actx_class(comm, queue,
                 allocator=cl_tools.MemoryPool(cl_tools.ImmediateAllocator(queue)),
-                force_device_scalars=True,
-                comm_tag_to_mpi_tag={
-                    _WaveStateTag: 1234,
-                    })
+                force_device_scalars=True)
 
     from meshmode.distributed import MPIMeshDistributor, get_partition_by_pymetis
     mesh_dist = MPIMeshDistributor(comm)

grudge/array_context.py

@@ -32,8 +32,7 @@
 # {{{ imports
 
 from typing import (
-        TYPE_CHECKING, Mapping, Tuple, Any, Callable, Optional,
-        Hashable, Type)
+        TYPE_CHECKING, Mapping, Tuple, Any, Callable, Optional, Type)
 from dataclasses import dataclass
 
 from meshmode.array_context import (
@@ -240,36 +239,24 @@ def __init__(self,
             queue: "pyopencl.CommandQueue",
             *, allocator: Optional["pyopencl.tools.AllocatorInterface"] = None,
             wait_event_queue_length: Optional[int] = None,
-            force_device_scalars: bool = False,
-            comm_tag_to_mpi_tag: Optional[Mapping[Hashable, int]] = None) -> None:
+            force_device_scalars: bool = False) -> None:
         """
         See :class:`arraycontext.impl.pyopencl.PyOpenCLArrayContext` for most
         arguments.
-
-        :arg comm_tag_to_mpi_tag: A mapping from symbolic tags used
-            in the *comm_tag* argument of
-            :func:`grudge.trace_pair.cross_rank_trace_pairs` to numeric values
-            to be used with MPI.
         """
         super().__init__(queue, allocator=allocator,
                 wait_event_queue_length=wait_event_queue_length,
                 force_device_scalars=force_device_scalars)
 
         self.mpi_communicator = mpi_communicator
 
-        if comm_tag_to_mpi_tag is None:
-            comm_tag_to_mpi_tag = {}
-
-        self.comm_tag_to_mpi_tag = comm_tag_to_mpi_tag
-
     def clone(self):
         # type-ignore-reason: 'DistributedLazyArrayContext' has no 'queue' member
         # pylint: disable=no-member
         return type(self)(self.mpi_communicator, self.queue,
                 allocator=self.allocator,
                 wait_event_queue_length=self._wait_event_queue_length,
-                force_device_scalars=self._force_device_scalars,
-                comm_tag_to_mpi_tag=self.comm_tag_to_mpi_tag)
+                force_device_scalars=self._force_device_scalars)
 
 # }}}
 

grudge/trace_pair.py

@@ -492,16 +492,20 @@ def cross_rank_trace_pairs(
             if isinstance(comm_tag, int):
                 num_tag = comm_tag
 
-            from grudge.array_context import MPIPyOpenCLArrayContext
-            if isinstance(actx, MPIPyOpenCLArrayContext):
-                num_tag = actx.comm_tag_to_mpi_tag.get(comm_tag)
-
             if num_tag is None:
-                raise ValueError("Encountered unknown symbolic tag "
-                        f"'{comm_tag}'. To make this symbolic tag work, "
-                        f"use 'grudge.array_context.MPIPyOpenCLArrayContext' and "
-                        "assign this tag a numerical value via its "
-                        "comm_tag_to_mpi_tag attribute.")
+                # FIXME: This isn't guaranteed to be correct.
+                # See here for discussion:
+                # - https://github.com/illinois-ceesd/mirgecom/issues/617#issuecomment-1057082716  # noqa
+                # - https://github.com/inducer/grudge/pull/222
+                from mpi4py import MPI
+                tag_ub = MPI.COMM_WORLD.Get_attr(MPI.TAG_UB)
+                num_tag = hash(comm_tag) % tag_ub
+
+                from warnings import warn
+                warn("Encountered unknown symbolic tag "
+                        f"'{comm_tag}', assigning a value of '{num_tag}'. "
+                        "This is a temporary workaround, please ensure that "
+                        "tags are sufficiently distinct for your use case.")
 
             comm_tag = num_tag
 

test/test_mpi_communication.py

@@ -46,7 +46,10 @@
 from pytools.obj_array import flat_obj_array
 
 import grudge.op as op
-from testlib import SimpleTag
+
+
+class SimpleTag:
+    pass
 
 
 # {{{ mpi test infrastructure
@@ -86,8 +89,7 @@ def run_test_with_mpi_inner():
     if actx_class is MPIPytatoArrayContext:
         actx = actx_class(comm, queue, mpi_base_tag=15000)
     elif actx_class is MPIPyOpenCLArrayContext:
-        actx = actx_class(comm, queue, force_device_scalars=True,
-                comm_tag_to_mpi_tag={SimpleTag: 15000})
+        actx = actx_class(comm, queue, force_device_scalars=True)
     else:
         raise ValueError("unknown actx_class")